1. Field of the Invention
This invention relates to annular superconducting electro-magnets for use in magnetic resonance imaging (MRI) apparatus.
2. Description of Related Art
Such electro-magnets comprise annular windings which are immersed in liquid helium to produce the low temperatures necessary for superconductivity. Such annular electro-magnets afford a cylindrical space within which a patient is positioned, the space including a predetermined substantially spherical volume, hereinafter referred to as the imaging volume, of high homogeneity magnetic field produced by current in the annular windings.
One of the problems with known electro-magnet arrangements is that in order to provide a desirable degree of magnet field homogeneity and magnetic field strength in the imaging volume, annular electro-magnets having a comparatively long axial length are necessary. One consequence of this is that patients positioned therein tend to suffer from claustrophobia.